Abstract : Ontario Lacus is the largest lake of the whole southern hemisphere of Titan, Saturn-s major moon. It has been imaged twice by each of the Cassini imaging systems Imaging Science Subsystem ISS in 2004 and 2005, Visual and Infrared Mapping Spectrometer VIMS in 2007 and 2009 and Radar in 2009 and 2010. In this study, we take advantage of each imaging dataset to establish a global survey of Ontario Lacus- environment from 2005 to 2010. We perform a geomorphological mapping and interpretation of Ontario Lacus, mainly based on a joint analysis of VIMS and Radar SAR datasets, along with the T49 altimetric profile acquired in December 2008. The morphologies observed on Ontario Lacus are compared to landforms of a semi-arid terrestrial analog, which closely resembles Titan-s lakes: the pans of the Etosha Basin, located in Namibia. From this comparison, we infer that Ontario Lacus is an extremely flat depression where liquids, only located in the darkest areas in the Radar data, cover topographic lows where the -alkanofer- would raise above the depression floor. The rest of the depression appears rather as a muddy flat surface likely composed of a thick coating of photon-absorbing materials, explaining its still rather dark appearance in the infrared and radar data. We also determined whether surface changes occurred during the 5 years time interval between 2005 and 2010. We found that the depression contour is constant at the resolution of ISS and VIMS data, both being consistent with the depression contour derived from the Radar data. Our interpretation, in which the liquids are located only in some parts of Ontario Lacus, agrees with the lack of significant change of the depression contour between 2007 and 2005 with more uncertainties and 2010.